Fuel cells electrochemically convert fuels and oxidants to electricity. Furthermore, fuel cells can be categorized according to the type of electrolyte (e.g., solid oxide, molten carbonate, alkaline, phosphoric acid, or solid polymer) used to accommodate ion transfer during operation.
A Proton Exchange Membrane (hereinafter "PEM") fuel cell converts the chemical energy of fuels such as hydrogen and oxidizers such as air/oxygen directly into electrical energy. The PEM is a solid polymer electrolyte that permits the passage of protons (H.sup.+ ions) from the "anode" side of a fuel cell to the "cathode" side of the fuel cell while preventing passage therethrough of the hydrogen and air/oxygen gases. Some artisans consider the acronym "PEM" to represent "Polymer Electrolyte Membrane." The direction, from anode to cathode, of flow of protons serves as the basis for labeling an "anode" side and a "cathode" side of every layer in the fuel cell, and in the fuel cell assembly or stack.
An individual PEM-type fuel cell generally has multiple, transversely extending layers assembled in a longitudinal direction. In the fuel cell assembly or stack, all layers that extend to the periphery of the fuel cells have holes therethrough for alignment and formation of fluid manifolds. Further, gaskets seal these holes and cooperate with the longitudinal extents of the layers for completion of the fluid manifolds. As is well-known in the art, some of the fluid manifolds distribute fuel (e.g., hydrogen) and oxidizer (e.g., air/oxygen) to, and remove unused fuel and oxidizer as well as product water from, fluid flow plates which serve as flow field plates of each fuel cell. Also, other fluid manifolds circulate coolant (e.g., water) for cooling.
As is well-known in the art, the PEM can work more effectively if it is wet. Conversely, once any area of the PEM dries out, the fuel cell does not generate any product water in that area because the electrochemical reaction there stops. Undesirably, this drying out can progressively march across the PEM until the fuel cell fails completely. So, the fuel and oxidizer fed to each fuel cell are typically humidified. Furthermore, a cooling mechanism is commonly employed for removal of heat generated during operation of the fuel cells.
The PEM can be made using, for instance, a polymer such as the material manufactured by E. I. Du Pont De Nemours Company and sold under the trademark NAFION.RTM.. Further, an active electrolyte such as sulfonic acid groups is included in this polymer. In addition, the PEM is available as a product manufactured by W.L. Gore & Associates (Elkton, Md.) and sold under the trademark GORES-ELECT.RTM.. Moreover, a catalyst such as platinum which facilitates chemical reactions is applied to each side of the PEM. This unit is commonly referred to as a membrane electrode assembly (hereinafter "MEA" ). The MEA is available as a product manufactured by W.L. Gore & Associates and sold under the trade designation PRIMEA 5510-HS.
In a typical PEM-type fuel cell, the MEA is sandwiched between "anode" and "cathode" gas diffusion layers (hereinafter "GDLs") that can be formed from a resilient and conductive material such as carbon fabric. The anode and cathode GDLs serve as electrochemical conductors between catalyzed sites of the PEM and the fuel (e.g., hydrogen) and oxidizer (e.g., air/oxygen) which each flow in respective "anode" and "cathode" flow channels of respective flow field plates.
A given fluid flow plate can be formed from a conductive material such as graphite. Flow channels are typically formed on one or more faces of the fluid flow plate by machining. As is known in the art, a particular fluid flow plate may be a bipolar, monopolar, anode cooler, cathode cooler, or cooling plate.
In order to fabricate a fluid flow field plate, one known configuration utilizes two outer layers of compressible, electrically conductive material and a center metal sheet interposed therebetween. Such a design is disclosed in U.S. Pat. No. 5,527,363 to Wilkinson et al. (entitled "Method of Fabricating an Embossed Fluid Flow Field Plate," issued Jun. 18, 1996, and assigned to Ballard Power Systems Incorporated and Daimler-Benz AG) and divisional U.S. Pat. No. 5,521,018 to Wilkinson et al. (entitled "Embossed Fluid Flow Field Plate for Electrochemical Fuel Cells," issued May 28, 1996, and assigned to Ballard Power Systems Incorporated and Daimler-Benz AG). In particular, the outward face of each of the two outer layers is embossed with flow field channels. These embossed outward faces serve as the two major faces for the fluid flow field plate.
However, existing fluid flow plate constructions require disadvantageously large usage of material for their formation. Moreover, such fluid flow plates add undesirable weight to the fuel cell assembly. Thus, a need exists for decreasing material usage in fuel cell assemblies.